All those results look unrealistically low (I myself frequently visit some of those sites, and I get votes almost daily on different questions and answers, new postings acquire more votes in one day than there are visits). What is going on here? And why is the number of vpd an integer and not a real?

Apologies for the slow response here in completely resolving the issue. We made major changes to our Google Analytics infrastructure a few months back and completely missed that the same GA properties were used to drive the metrics behind Area51 stats and overall site analytics.

When we finally made the cut over to our new GA properties it coincided with the final couple of sprints before launching Teams so my time (and DAG's time) was completely tied up elsewhere.